Some unclear points about self-oscillation

msddw

Some unclear points about self-oscillation [Copy link]

 

1. Why is the starting condition of self-oscillation |AF|>1? How is it calculated? 2. Why is it easier to self-oscillate when the feedback depth is greater? Please answer this question, I don’t understand it.

msddw

Also, does self-oscillation require the phase condition or the amplitude condition to be met first?

maychang

When |AF|<1, any fluctuation in the circuit will be smaller than the original fluctuation after amplification and feedback, so oscillation cannot be maintained.

maychang

msddw posted on 2019-4-29 11:47 Also, does self-oscillation need to satisfy the phase condition or the amplitude condition first?

"Does self-oscillation need to satisfy the phase condition or the amplitude condition first?" Both must be satisfied.

冀秀波

Doesn’t the general design take into account the zero-crossing point of the phase-frequency characteristic of the Bode plot?

msddw

maychang published on 2019-4-29 12:10 "Does self-oscillation need to satisfy the phase condition or the amplitude condition first?" Both must be satisfied.

Why is it said that the amplitude condition is a sufficient condition for self-oscillation, and the phase condition is a necessary condition for self-oscillation? What is the relationship between the depth of negative feedback and self-oscillation?

maychang

msddw published on 2019-4-29 13:08 Why is it said that the amplitude condition is a sufficient condition for self-oscillation, and the phase condition is a necessary condition for self-oscillation? Negative feedback depth and self-oscillation...

"Why is it said that the amplitude condition is a sufficient condition for self-oscillation, and the phase condition is a necessary condition for self-oscillation?" "The amplitude condition is a sufficient condition for self-oscillation", who said this?

maychang

I have posted several posts: Miscellaneous Talks on Sine Oscillator Circuits (I) Miscellaneous Talks on Sine Oscillator Circuits (II) Miscellaneous Talks on Sine Oscillator Circuits (III) Maybe they can help with your problem.

msddw

maychang published on 2019-4-29 13:31 "Why is it said that the amplitude condition is a sufficient condition for self-oscillation, and the phase condition is a necessary condition for self-oscillation?" "The amplitude condition is a sufficient condition for self-oscillation...

https://wenku.baidu.com/view/b7a97d050740be1e650e9ab5A conclusion in this document

msddw

maychang published on 2019-4-29 13:31 "Why is it said that the amplitude condition is a sufficient condition for self-oscillation, and the phase condition is a necessary condition for self-oscillation?" "The amplitude condition is a sufficient condition for self-oscillation...

https://wenku.baidu.com/view/b7a97d050740be1e650e9ab5I read it here, and it says this is a conclusion

maychang

msddw published on 2019-4-29 14:33 https://wenku.baidu.com/view/b7a97d050740be1e650e9ab5 A conclusion in this document

The title of this PPT document is "Self-oscillation and Elimination of Negative Feedback Amplifier Circuit". Self-oscillation occurs in the negative feedback amplifier, which cannot work normally. The self-oscillation in the negative feedback amplifier is an abnormal working state that we do not need. Moreover, the first page of the PPT is the phasor expression, which expresses both the amplitude-frequency and phase-frequency conditions at the same time, and has completely answered the question "Does the self-oscillation need to meet the phase condition or the amplitude condition first?" Therefore, the statement on page 5 of the PPT that "amplitude condition is a sufficient condition for self-oscillation, and phase condition is a necessary condition for self-oscillation" is wrong. Sufficient condition means that once the condition is met, self-oscillation will occur.

maychang

msddw posted on 2019-4-29 14:38 https://wenku.baidu.com/view/b7a97d050740be1e650e9ab5 I saw it here, and it says this is a conclusion

"I saw it here, and it says this is a conclusion" You should first clarify the "sufficient conditions" and "necessary conditions" as well as "necessary and sufficient conditions".

maychang

msddw posted on 2019-4-29 14:38 https://wenku.baidu.com/view/b7a97d050740be1e650e9ab5 I read it here, and it says this is a conclusion

"Sufficient conditions" and "necessary conditions" and "sufficient and necessary conditions" are the contents of middle school mathematics. If you still have doubts about "sufficient conditions" and "necessary conditions" and "sufficient and necessary conditions", just Baidu.

msddw

Got it, thank you teacher

witin

So lively...